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11
TROUBLESHOOTING
No.
Symptom
1
The systems are
not switched
when
communication
error occurs.
2
The systems are
consecutively
switched.
3
When using the
redundant IP
mode, the
MODBUS/TCP
master cannot
communicate
with the
QJ71MT91 of
the new control
system after a
system
switching.
11 - 6
Check Item
Is the standby system CPU module
operating normally?
Is the tracking cable connected
properly?
Has the QJ71MT91 issued a system
switching request to the standby
system CPU module?
Is there any cause, such as a standby
system CPU module stop error, which
disables system switching even when
the QJ71MT91 issues a system
switching request?
Are the parameter and program
written in the Redundant CPU in the
backup mode?
Is the value of the timeout occurrence
time too small?
Is the QJ71MT91 used as the
MODBUS/TCP master?
Is the Gratuitous ARP disabled in a
security software setting (ARP
spoofing measures) on the
MODBUS/TCP master side?
Corrective Action
• Check if the power supply module of
the standby system is powered on.
• Check if the RESET/L.CLR switch of
the standby system CPU module is
set to the central position (reset
clear).
• Check if no error is occurring in the
standby system CPU module.
Connect the tracking cable properly.
Issue a system switching request to
the control system CPU module.
Remove the cause of the system
switching failure in the standby system
CPU module.
Change the parameter and program to
the backup mode and write them to
the Redundant CPU.
Increase a timeout occurrence time to
an acceptable value as a system.
Use the fixed IP mode when using the
QJ71MT91 as the MODBUS/TCP
master. (The redundant IP mode
cannot be used.)
• Check if the MODBUS/TCP master
device supports the Gratuitous ARP.
• Review the security software
settings on the MODBUS/TCP
master side.
• Review the security software
settings on the MODBUS/TCP
master side.
• Use the fixed IP mode.
MELSEC-Q
Reference
Section
11 - 6
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